The first steps of this project are to produce the recombinant protein, investigate refolding conditions and develop a process for purifying the refolded recombinant protein.[unreadable] A gene encoding the Plasmodium falciparum Circumsporozoite (CS) protein has been designed, synthesized, and cloned into an E. coli expression vector. A clone expressing the recombinant CS protein (rCSP) was selected. The rCSP, expressed as inclusion bodies, has an intact N-terminus and is being characterized for disulfide linkages. The current effort is to develop a process for scaled production of the rCSP. Efforts are also being made to produce the CSP in the Pichia pastoris expression system.[unreadable] We have generated several monoclonal antibodies (mAbs) using the C-terminal domain of a yeast produced CS protein as immunizing antigen. Six mAbs recognized the sporozoites and the native CS protein. Three of them are conformation-dependent mAbs, recognizing at least 2 independent epitopes. The other 3 mAbs recognized the CS repeats and are thus conformation independent. Two of these antibodies have the ability to inhibit sporozoite invasion of HepG2 cells in an in vitro assay.[unreadable] A mouse model using a transgenic berghei parasite expressing falciparum CSP on its sporozoite surface is being developed and tested as an assay to evaluate protection imparted by a CSP-based vaccine. We have also created an expression construct to generate a transgenic knowelsi parasite, expressing falciparum CSP on its sporozoite surface. This transgenic parasite, once obtained, will be used to establish a rhesus model to evaluate protection imparted by a CSP-based vaccine in monkeys.